The objective of this proposal is to improve our understanding of the mechanism of chronic rejection of renal allografts. Its main focus is upon idiotypic network regulation of the immune response to HLA, including fundamental aspects of the humoral and cellular mechanism of rejection and its immunogenetic control. Specific Aim #1 is to determine whether the length of allograft survival is influenced by anti-idiotypic antibodies develop by the recipient prior to transplantation. Specific Aim #2 is to determine the relevance of Ab2, developed following transplantation to long-term function of the graft and to establish whether the presence of free or complexed Ab1 and soluble donor HLA antigens is indicative of rejection. Sensitized patients will be evaluated for the presence of Ab2 prior to transplantation. The post-transplantation follow-up will include patients who have tolerated the graft for 1 to 10 years. Patients will be tested for anti-HLA antibodies (Ab1) following depletion of soluble HLA antigens. The specificity of anti-donor Ab1 in sera with multiple cytotoxic antibodies, will be evaluated. The presence of Ab2 or Ab3 will be assess from the Ab1 inhibitory or Ab1-augmenting activity of patients' sera, respectively. Soluble HLA antigens from the graft will be primarily measured by cytotoxicity inhibition studies using murine monoclonal antibodies to well defined donor HLA class I antigens. Other soluble HLA antigens from the graft will also be investigated. Immune complexes of recipient Ab1 with HLA graft antigens will be dissociated by immunoaffinity on magnetic beads coupled with murine MoAb to human HLA, and the released Ab1 and alloantigen will be tested by cytotoxicity and immunofluorescence methods. The value of these tests for predicting and monitoring the onset of rejection and stage of maturation and functional characteristics of alloreactive T and B cells from renal allograft recipients. The frequency of activated T and B lymphocytes will be determined using as markers the NDA3, NDA4 and LDA1 antigens. The memory potential of alloreactive T cells and their helper, amplifier and suppressor function will be ascertained. The memory potential of activated B cells will be ascertained from the frequency of Ab1 and Ab2 producing cells. Network interactions between the T and B cells will be evaluate by studying the ability of patient T cells to induce maturation of Ab1 and Ab2 producing cells. Specific Aim #4 is to determine whether the immune response to HLA in cyclosporine treated renal allograft recipients is controlled by Ir genes. The recipients HLA-DR. DO and DP genotype will be established by RFLP and oligonucleotide typing. Positive associations between distinct genotypes and production of Ab1, Ab2, Ab3, frequency of rejection episodes and allograft survival will be determined. This project may contribute to the development of new tools for treatment and early diagnosis of chronic rejection.